We seek to determine whether common air pollutants such as singlet molecular oxygen be implicated in the oxidation of unsaturated lipids of cellular membranes. The matter will be examined using cholesterol and isomeric stenols such as cholest-4-en-3 Beta-ol and 5alpha-cholest-7-en-3Beta-ol as specific trapping agents of singlet oxygen, from which unique oxidation products obtain. The oxidation of the selected stenol trapping agents will be studied in biological systems using human or animal membranes and cells exposed to oxidants including polluted air and singlet oxygen, and in model systems which simulate human tissues. Sterol oxidation products will be detected and identified by sophisticated chromatographic and spectral methods. The identity of the oxidation products can then be used to determine whether singlet oxygen as involved or whether some other oxidizing agent caused formation of the oxidized sterols found. Other oxidants to be considered are superoxide radical anion, hydrogen peroxide, and free radical reactions of ground-state oxygen. All oxidized sterols implicated in these oxidations will be sought and analyses for them will lead to decisions regarding the specific oxidizing species responsible. We shall have for the first time a means of specifically determining the initial oxidation event in a complex series of events leading to extensive lipid peroxidations and membrane damage generally resulting in loss of function, lysis, and cell death in tissues exposed to unsuspected sources of oxidizing agents.